Re: sh: -c: line 0: syntax error near unexpected token `('

Looks like sh on your system is not bash (or any shell that supports the process substitution syntax).

-derby

Update: You could always force bash:

$RT_DiffFiles= `bash -c \"comm -23 <(sort $RT_64OG_FilesPath) <(sort $
+RT_64_FilesPath)\"`;
[download]

but I'd look to see if Text::Diff accomplishes what you're after first.